The motion put before Parliament this autumn on the final Brexit agreement will be amendable by MPs and its outcome will be binding on the government, David Davis has said.

The Brexit secretary said the motion - which prime minister Theresa May has previously described as a "take it or leave it" choice - would relate to a political agreement expected to be reached with Brussels, rather than a full legal treaty.

But he said it remained the government's intention to have a treaty ready for signing immediately after the formal date of Brexit on March 29, 2019.

The confirmation that the government's motion will be amendable opens the door to opponents of Brexit seeking to force a vote on a second referendum, or for Labour to demand that ministers go back and renegotiate a bad deal.

Giving evidence to the Commons Brexit committee, Mr Davis played down suggestions that the government's proposals for the Irish border had run into the sand.

Reports last week suggested that Brussels had dismissed as unworkable both of the options put forward by London, which would either see the UK collect customs tariffs on behalf of the EU or use technology to avoid delays at the border.

The reports sparked speculation that Brussels was trying to edge the UK into remaining in some form of customs union with the EU - something which committee Brexiteers regard as unacceptable, as it would prevent Britain from forging new trade deals elsewhere in the world.

Mr Davis rejected committee chairman Hilary Benn's suggestion that the UK solutions had been "emphatically" ruled out by Brussels, insisting that the EU was simply setting out an "opening position" in negotiations.

He told the committee that the technology to deliver a near frictionless border - including number-plate recognition, authorised economic operator systems and electronic pre-authorisation - already existed and the Government had started talks with potential suppliers.

Mr Davis was speaking ahead of a meeting this afternoon of a cabinet sub-committee dubbed Mrs May's "Brexit war cabinet", which will bring together senior ministers to drive negotiations forward in the vital coming months.

It is understood that the customs union is not on the formal agenda, but the issue is expected to test cabinet unity to the utmost as the sub-committee meets in the coming weeks, with senior Brexiteers like Boris Johnson and Liam Fox understood to be wary of any concession.

Addressing the Brexit committee, Mr Davis restated government promises of a "meaningful vote" on the final deal, but confirmed that MPs and peers were likely at that stage to be presented with "a political declaration rather than a treaty draft".

Asked by Mr Benn whether the motion would be amendable, the Brexit Secretary replied: "If you can tell me how to write an unamendable motion, I will take a tutorial."

And pressed on whether ministers will regard the outcome as binding, Mr Davis said: "The government is unlikely to put a vote to the House which it doesn't intend to take properly seriously. If the House rejects the proposed negotiation, that negotiation will fall."

Further votes could then be expected on any treaties which emerge from the process, which could include a separate pact on security and defence as well as the main agreement on economic relations, he said.

Mr Davis said suggestions that Parliament was not being given enough time to debate Brexit were "at odds with reality".

He insisted there was "no absence of information" on the exit process.

The Brexit secretary said it was "unlikely" there would be a no-deal outcome from the negotiations but there could be a "bare bones" agreement.

"I do not think no deal is a significant probability at all," he added.

Mr Davis said it was his "hope" that the first trade deal could come into force the day after the UK leaves.

Asked if there was a risk of Britain staying in the customs union for an indefinite period while an problems with customs were resolved, he replied: "I do not expect the solution to that to be extension of membership of the customs union.

"I would view that on my part as a failure."

The Brexit secretary insisted the deal that was agreed by October would be "substantive".

"We will be voting for a bill of £35-£39 bn. People want to know on the other side what we are getting in exchange.

"The hardest time I'm going to have in October is people saying 'what have we got for this?"'

He dismissed suggestions that discussions about future trade arrangements because of problems to find a solution to the Irish border problem.

Mr Davis brushed aside reports that the European Council had set a deadline of June for a final decision on the Irish border.

The Brexit Secretary has previously suggested he was looking to October for an agreement.

He told the committee: "In negotiations, people try to set up deadlines - sometimes artificial deadlines - to put pressure on an element of the negotiation which they think is in their favour."

Mr Davis said he agreed with Irish Taioseach Leo Varadkar that a good agreement in October was better than any agreement in March.

Labour committee member Stephen Kinnock said that Mr Davis's confirmation that the motion to be put before MPs will be amendable had set the country on track for a potential "constitutional crisis".

"To be clear, if the House amends the motion and instructs the government to go back to Brussels and negotiate a different deal to the one that was put before us, the government would respect the will of the House and go back to Brussels do that?" asked Mr Kinnock.

Mr Davis did not rule out the possibility, saying only: "I'm not going to speculate on amendments that have not even yet been laid, let alone been passed by the House."

Mr Kinnock said: "Surely you must appreciate the risk of us heading towards a constitutional crisis here? And surely it's the responsibility of the government to have scenarios in mind so that it is ready to respond when the House does vote?"

Mr Davis responded: "I'm not going to give advice on how to create circumstances which may undermine the government's negotiating position.

"I'm not entirely sure how much force a government sent back with its tail between its legs by Parliament would have in such a negotiation."

Mr Davis denied suggestions the government was "winging it" over Brexit.

"No, we are not winging it but we are having to accommodate different changes as we go along," he said.

The Brexit secretary insisted there would not be a repeat of the Windrush scandal with the children of EU citizens living in Britain.

"At the risk of being mildly self-righteous I'll point you to my own speeches early on in this process where I said our treatment of the European citizens in the UK would be a moral issue, it was a moral imperative and that is how we will treat it," he said.

Mr Davis dismissed suggestions that the government's own modelling showed the potential from future trade deals did not outweigh the benefits of being in the EU.

"The modelling is based on guesses on what will happen to our trade deals," he said.

Mr Davis said he had been "not particularly enamoured" with mathematical modelling techniques because they "sit on assumptions of what will happen to trade".

"If you get that assumption wrong, the whole model is wrong," he said.

"The best modelling in the world is wrong."

He said the formercChancellor George Osborne had previously found £26bn was "found down the back of the sofa" because the modelling had been wrong.

Committee chairman Hilary Benn rebuked the Brexit secretary for having to cut short the hearing to attend another meeting.

He told Mr Davis: "It's not satisfactory to be told, having fixed a date, having taken time for your office to be able to find, and we recognise there are pressures upon you, then to be told there's a time constraint."

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